The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
An existing heat-pump type of laundry dryers (i.e., laundry dryers) is provided with an air circulation passageway as follows: heated air heated by a condenser in a heat pump circulation system is delivered to a drying chamber having clothes therein, wet air obtained after taking moisture from the clothes is delivered back to an evaporator for dehumidification, and air obtained after dehumidification is again heated by the condenser and is then sent into the drying chamber.
In a drying system of a heat-pump laundry dryer, tolerant pressure of a compressor system is saturation pressure of a refrigerant at a temperature between 60 to 70° C. At a drying post stage, a condensing temperature of the compressor approaches a limit value of peak pressure with increase of temperature. An existing drum-type, heat-pump laundry dryer is designed with an auxiliary condenser and an auxiliary fan, so to assist an operation of a fan at a drying post stage or in a high-temperature environment, for regulating a load of a compressor.
Chinese Patent Application No. 200610153406.9 discloses a laundry dryer capable of enabling a heat pump that generates drying air circulated between a drying chamber and the heat pump to operate stably. Air heated by a heater in the heat pump is delivered to a water barrel used as the drying chamber. Air discharged from the water barrel returns back to the heat pump after passing through a filter unit, and is then dehumidified by a heat absorber and again delivered to the heater to form an air circulation passageway. The filter unit is provided with a lint filter, and is provided with a duct communicating with an air outlet and an air inlet.
Chinese Patent Application No. 200410097855.7 discloses a laundry dryer including: a heat pump device; an air path for guiding drying air into a heat absorber and a heat radiator of the heat pump device and a drying chamber having therein clothes; a blower for blowing the drying air to the air path; and a control device. In a process of drying clothes, a compressor and a blower operate. If the process of drying clothes is interrupted, the control device stops the compressor for a prescribed time.
For the above heat pump drying type of the laundry dryer, in an environment with a high temperature, for example, in an environment with a temperature between 35 to 40° C., the temperature of air that blows into a washing/drying barrel rapidly increases to above 60° C. at a drying start stage, and the temperature and humidity of air that blows out from the washing/drying barrel also increase rapidly. In this situation, saturation pressure of a refrigerant in an evaporator is high, a load of a compressor system is great, and a critical working pressure of the compressor is reached rapidly.
For a laundry dryer using a variable-frequency compressor system, although working frequency of a compressor may be adjusted by a control system for the compressor for regulating a working load of the compressor and running frequency of the compressor may be reduced along with an increase in temperature in a barrel to save power consumption, a lowest working frequency of the variable-frequency compressor in the existing laundry dryer is a preset value within a range that the compressor permits and when the temperature in the barrel increases and it is necessary to further reduce the running frequency, the running frequency cannot be further reduced after the preset lowest value is reached.
When there is a small amount of clothes in a drum, the volume occupied by the clothes occupy is small; for the compressor to achieve a same condenser surface temperature, that is, for a same cylinder intake temperature, a circulated air volume becomes larger since a blocking effect of the clothes is small, a cylinder outlet temperature is higher than that of clothes of a large volume, and an average temperature in the whole drying barrel is high. Moreover, the clothes are relatively loose when the occupied volume is small, and moisture in the clothes can easily evaporate. When there is a larger amount of clothes in the drum, the volume occupied by the clothes is large; for the compressor to achieve a condenser surface temperature the same as the above condenser surface temperature for drying the small amount of clothes, that is, for a same cylinder intake temperature, a circulated air volume becomes smaller since a blocking effect of the clothes is great, a cylinder outlet temperature is lower than that of the clothes of the small volume, and an average temperature in the whole drying barrel is high. Besides, since there is a large amount of clothes, tightly twined with each other, moisture in the clothes cannot easily evaporate. If a same compressor rotation rate as one for drying clothes of a small volume is used, an average drying time for per unit of weight becomes longer, and average power consumption becomes greater.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.